1. Field of the Invention
The present invention generally relates to remotely identifying and locating items by using radio frequency signaling and, more particularly, to remotely identifying and locating a specific item from among many items by using both radio frequency signaling and optical signaling.
2. Description of the Related Art
Radio frequency identification (RFID) tags are now in common use with many goods or items. An RFID tag is an electronic device attached to an item or object and contains a unique identifier, e.g., an identification (ID) number, that can be interrogated and read remotely using a radio frequency (RF) signal. When the RFID tag is interrogated by an interrogator of an RFID tag reader, the tag responds with at least its unique identifier.
Many different types of RFID tags are now in use. For example, and not intended to be limiting: some tags are substantially passive, that is, they do not emit a signal but their presence in a field of an antenna of the reader dynamically alters the impedance of the antenna allowing their presence to be detected; some are semi-passive, that is, they receive a signal from the interrogator on a first frequency and use the received energy to reply on a second frequency; and some are active, that is, they have an on-board power source for the tag, which is turned on by a signal from the interrogator so that the tag can broadcast a response.
The tag identifier therefore identifies the item with which the tag is associated. When the tags are within a signaling range of the interrogator, they respond. If the unique identifier of the desired item is among those scanned by the interrogator, then a user will know that the desired item is present within the signaling range of the interrogator.
RFID tags are finding many useful applications in finding and identifying items, but there are some applications where bar code symbols on items provide a finding and identifying functionality that RFID tags cannot match. One such situation occurs when a specific item must be located in a warehouse full of items, or on a shelf stocked with many items in a retail establishment. In a warehouse picking application, a picker manually gathers various items from the shelves in a warehouse to fulfill specific orders. The picker is instructed to find a specific shelf location, and to pick a specified number of a particular item from the shelf. To minimize the chance of error, the picker is often required to scan a bar code symbol located on a label on the shelf, or on the item, to indicate to a computerized tracking system that the picker has indeed located the correct item. Unless the picker does this, the picker is not given the location of the next item to be picked, and so the picker cannot proceed without verifying that each item has been properly located.
Electro-optical readers for scanning and reading the bar code symbols used in these picking applications are often worn on the picker's finger, like a ring, or strapped to the back of the picker's hand, in order to enable the picker to manually grasp and pick up the items. The symbol readers have a working distance range of about a foot or more, thereby making it easier for the pickers to aim the readers at the symbols on items located on high or low shelves without excessive bending or reaching. Shelf labels on warehouse shelves are often packed closely together, but since a symbol reader can easily be aimed at a specific symbol, there is no doubt in the mind of the picker about which symbol has been scanned, and so the picker knows exactly which item should be picked.
Picking is sometimes done by personnel walking around the warehouse, and sometimes by operators riding in and operating forklifts, especially where the items that are being picked are very large, bulky or heavy. When an operator is on a forklift, the electro-optical symbol reader needs an even greater range of working distances, so that the operator does not have to get off the forklift to get close enough to the symbol to scan it with the reader.
RFID tags have been unable to replace bar code symbols in this kind of picking application because, unlike bar code symbol readers, it is not possible to aim the RFID reader at a specific tag and interrogate and read only the tag at which the RFID reader is aimed, and not also interrogate and read neighboring tags. If the RFID reader interrogates a neighboring tag, then a user will not know which RFID tag has been interrogated, and might pick the wrong item from the shelf.
One way to solve this problem with existing RFID technology is to reduce the interrogating range or sensitivity of the RFID reader to the point that it only has a few inches of range. This allows the RFID reader to read only a single RFID tag that might be within this limited interrogating range. However, if the RFID tags are very close together, then the interrogating range may have to be reduced to essentially zero to avoid possible mistakes. Unfortunately, when the interrogating range is reduced so much, it becomes very inconvenient for the user to interrogate tags on high and low shelves, or to otherwise locate a specific RFID tagged item that is not easily reached. It is even more inconvenient for those users on forklifts.
If this problem could be solved, RFID tags could be used to solve problems that only bar code symbols solve today. In fact, in the example given above, RFID technology could actually provide advantages over bar code reading technology, which could help justify the higher cost of RFID tags. For example, since RFID tags can be interrogated from a distance, even when out of a line of sight of the RFID reader, an RFID reader mounted on a forklift could start interrogating a desired tag as the forklift approaches, assuring the operator that he or she is heading towards the desired item. Of course, other neighboring tags would also be interrogated, but the operator would still know that he or she is in the right neighborhood to find the specific item being looked for. Once the operator arrives at the right place, however, the operator would still need to be able to interrogate only the desired tag, and ideally this would be accomplished without getting off the forklift. Hence, there is an advantage to have RFID readers that are capable of interrogating many tags at once, and are also capable of interrogating, or locating a specific tag.